1. Field of the Invention
This invention relates to feedback systems used to control both the throttle valve of an internal combustion engine and the ratio setting of an associated continuously variable transmission, usually in response to the position of the accelerator pedal in a passenger car.
2. Description of the Prior Art
The prior art includes many systems for controlling the throttle setting and the transmission ratio in a passenger car equipped with a continuously variable transmission (C.V.T.). A few of these C.V.T. control systems can be recalibrated or slightly modified to implement the extensive wide open throttle engine operating schedule as advanced for improving fuel economy in U.S. Pat. No. 4,023,641. For instance, an appropriate change in cam profile will extend the invention disclosed in Canadian Pat. No. 665,093 to include a predominantly full throttle engine operating schedule. Nevertheless, such modifiable prior art systems have no provision for dealing with engine speed errors which result from a limited transmission ratio range. In other words, transmission ratio is used to limit full throttle engine operating speed, and thus also the engine power output. When the transmission reaches its most extreme overdrive ratio, however, both engine speed and power output may continue to climb well beyond their intended values. Engine power can still be regulated to the desired level, but only through bothersome manipulation of the accelerator pedal.
Recalibrated prior art systems would also have no provisions for the deviations from predominantly full throttle operation that are sometimes desirable for driveability and usually necessary for cold engine operation. Finally, the engine throttle valve is opened too abruptly relative to accelerator pedal movement when the prior art systems are modified to secure the fuel economy advantages of extensive wide open throttle engine operation.